Nematodes
Dagger Nematode (Xiphinema americanum)
Root-lesion Nematode (Pratylenchus penetrans and P. crenatus)
Insects & Invertebrates
Symptoms
Nematode damage can occur without above ground symptoms, though a gradual decline in yield over a period of years often indicates a problem. Virus transmission by dagger nematodes produce symptoms on leaves such as yellowing of veins, mosaic, and malformation of the plant. Poor growth and yellowish foliage are symptoms of root-lesion nematode. Yields may be reduced when nematode populations reach high levels.
Identification
Both dagger and root-lesion nematodes are microscopic and have a wormlike shape. They are found only in the soil.
Life History
Dagger nematodes have the life stages of egg, juvenile and adult. Juvenile stages are smaller than the adult stage. They reproduce once per year, live four or five years and reach highest population levels in undisturbed areas and in zones within soil where oxygen is most plentiful. Dagger nematodes are migratory ectoparasites; they do not enter plant tissue and instead feed on root cells from the outside, piercing cells to feed on the interior. Root-lesion nematodes are migratory endoparasites; they tunnel into the root to feed and return back to the soil.
Monitoring
Dig up plant roots and inspect for enlarged root tips and feeder roots resulting in a 'witches' broom' effect on the root. The roots may also appear discolored and without fine roots. To confirm presence of nematodes, send a soil sample to a diagnostic laboratory for identification. A soil test should be done before initial planting. The best time to sample for nematodes is December through March.
Management
Before planting, chemical treatment can be made. In an established planting, plants in the infested area should be removed and a spot fumigation cam be made. Plant virus tested, certified stock.
The use of soil solarization (using clear plastic over soil during the summer to heat the soil to a high temperature) has been used with some efficacy in the season before planting.
Web Resources
Oregon State University Extension, An Online Guide to Plant Disease Control, Root Lesion Nematodes
http://plant-disease.ippc.orst.edu/disease.cfm?RecordID=184
Oregon State University Extension, An Online Guide to Plant Disease Control, Dagger Nematodes
http://plant-disease.ippc.orst.edu/disease.cfm?RecordID=183
Oregon State University Extension, An Online Guide to Plant Disease Control, Nematodes
http://plant-disease.ippc.orst.edu/articles.cfm?article_id=1
Michigan State University, Michigan Blueberry Facts, Nematodes
http://www.blueberries.msu.edu/nematodes.htm
ATTRA, Nematodes: Alternative Controls
http://www.attra.org/attra-pub/nematode.html
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